1. Field of the Invention
The present invention relates to transmission control, and more particularly to a packet transmission control method and a packet transmission system for the same.
2. Description of the Related Art
At present, a W-CDMA system has been developed. The W-CDMA system is applied with a circuit switching system in which a channel or a spreading code is once secured by a voice signal user and continues to be possessed by the voice signal user, until the communication of a voice signal ends. The W-CDMA system can handle a data packet in addition to the voice signal such that the W-CDMA can cope with the Internet. In this way, the W-CDMA system is assumed as the system in which the circuit switching system and the data packet coexists. The structure of a transmitter of a downlink in the W-CDMA system is disclosed in xe2x80x9cEffects of Orthogonal Spreading and Rake Combining on DS-CDMA Forward Link in Mobile radioxe2x80x9d by Fumiyuki Adachi (IEICE Transactions on Communication Vol. E80-B, No. 11, November 1997).
FIG. 1 shows the transmission situation of signals in the downlink when the transmitter is used. All the signals are transmitted in parallel. D1, D2, . . . , D5 indicate data packet signal users and V1, V2, . . . , V4 show voice signal users, respectively. There are the following problems in this well known technique.
The first problem is in that the channel capacity of the down link is determined based on the number of existing spreading codes, and users who exceed the number of the spreading codes can not be permissible regardless of whether the users are voice signal user or packet signal users. The reason is that either of the voice signal user and the packet signal user must use a spreading code as an accessing user. In this way, the number of users who can use the system is actually limited to the number of spreading codes.
The second problem is that actual traffic quantity is less than the number of accessing users so that the capacity of the system is not sufficiently used. FIG. 1 shows an example of the voice signal users accessing at the same time and the traffic situation which actually occurs. The reason is that the channels are limited based not on the actual traffic quantity but on the number of accessing users, as seen from FIG. 1. In this way, the number of users who can actually use the system is limited based on the number of channels which is limited based on the system itself.
In conjunction with the above description, a communication resource allocation is described in Japanese Laid Open Patent Application (JP-A-Heisei 5-252101 corresponding to U.S. application filed on Nov. 1, 1991). In this reference, an allocating unit includes a unit for distinguishing a subscriber with the highest priority from among conflicting subscribers in a radio communication network. A usable communication resource is allocated to the distinguished subscriber in a short time with no relation to a traffic quantity without collision.
Also, a radio ATM-LAN transmission system is described in Japanese Laid Open Patent Application (JP-A-Heisei 10-32579). In this reference, a radio base station functions as a parent station with first and second units. The first unit manages resources in its service area using combinations of a spreading code and a chip rate in CDMA. The second unit allocates the resources based on the combination of a spreading code and a chip rate in accordance with a service request from a radio terminal in the service area or an ATM terminal on the side of ATM-LAN. The radio terminal receives a plurality of spreading codes and a plurality of chip rates from the parent station, and sets a spreading code and a chip rate to change a transmission rate to an optimal value.
Also, a spread spectrum communication apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 9-270767). In this reference, a primary modulating section (3, 4) multiplies a digital information signal from an input section (1, 2) with a carrier signal such as a sine wave to produce a narrow band signal. A secondary modulating section (5) multiplies the narrow band signal of a picture with a spreading code (a) to produce a spread signal (7). A secondary modulating section (6) multiplies the narrow band signal of a sound with a spreading code (b) to produce a spread signal (8). An adder adds the spread signal (7) and the spread signal (8). The spread spectrum communication apparatus further includes a transmission section (10), a transmission antenna (11) and a reception antenna (21). Also, a receiving section (22) produces a code multiple signal (24). A distributor (23) distributes the code multiple signal into two. A primary demodulating section (25) multiplies the spreading code a with the code multiple signal (24). A secondary demodulating section (26) multiplies the spreading code b with the code multiple signal (24). The spread spectrum communication apparatus further includes a second demodulating section (27, 28) and an output section (29, 30).
Also, a radio resource control method is described in Japanese Laid Open Patent Application (JP-A-Heisei 10-190621). In this reference, physical radio resources are divided into continuous frames in a time direction. The frame includes slots (16, 17, and 18) with various sizes. The slot indicates a predetermined allocation ratio of the physical radio resources contained in each frame, and can be individually allocated to different radio connections. The first dimension of the frame is a time and the second dimension of the frame is time, frequency or code. The slot indicates various sizes in the second dimension direction. A first predetermined integer of the first size slot can be exchanged in a modular with another integer of the slot with another size.
Also, a radio communication apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 10-112698 corresponding to U.S. application filed on Sep. 27, 1996). In this reference, a reduced gain spread spectrum communication system (6) includes transceivers (8) connected to a base station (10). Also, a spreading unit (28) is contained to spread a digital packet (26) indicative of sound using a spreading sequence length shorter than a spreading gain available to a predetermined transmission band. The spreading unit (28) can spread a digital packet indicative of a data using a spreading sequence length longer than the spreading sequence length for the sound.
Therefore, an object of the present invention is to provide a transmission system in which the number of users is not limited based on the number of spreading codes, and a transmission control method for the same.
Another object of the present invention is to provide a transmission system in which the number of users is not limited based on the number of channels, and a transmission control method for the same.
In an aspect of the present invention, a packet transmission control method is achieved by borrowing a first channel of a plurality of channels from a first one of a plurality of existing users in response to a packet receiving request, and by transmitting packets to a new user using the first channel.
Here, in the borrowing, a receiving operation by the first existing user may be stopped in response to the packet receiving request from the new user.
Also, in the borrowing, a spreading code may be allocated to the new user in response to the packet receiving request from the new user. At this time, in the transmitting, the packets is transmitted to the new user using the first channel and the allocated spreading code.
It is preferable that the first channel is a voice channel. In this case, in the borrowing, the first channel may be monitored in response to a monitor request generated in response to the packet receiving request, and a receiving operation by the first existing user is stopped when a voiceless portion of the first channel is detected. Also, in the transmitting, a receiving operation by the new user may be stopped when a voice portion of the first channel is detected after the voiceless portion of the first channel is detected. In addition, the receiving operation by the first existing user is restarted when the voice portion of the first channel is detected after the voiceless portion of the first channel is detected. In addition, in the borrowing, a spreading code which is allocated to the first existing user may be allocated to the new user in response to the packet receiving request from the new user.
Alternatively, it is preferable that the first channel is a data channel. In this case, in the borrowing, a time slot and a spreading code which is allocated to the first existing user may be allocated to the new user in response to the packet receiving request from the new user. Also, in the transmitting, packets to the first existing user are delayed while the packets are transmitted to the new user using the allocated time slot and the allocated spreading code.
Also, in the packet transmission control method, another channel is borrowed for another existing users, when the channel is used for the existing user, and other packets are transmitted to the new user using the other channel.
In order to achieve another aspect of the present invention, a packet transmission control apparatus, includes a control unit and a base station. The control unit monitors a transmission situation to an existing user via a channel in response to a monitor request, and controls a new user to receive packets. The base station outputs the monitor request to the control unit in response to the packet receiving request from the new user, and transmits the packets to the new user in response to the control to the new user by the control unit.
When the first channel is a voice channel, the control unit may control the existing user to stop a receiving operation when the control unit detects a voiceless portion of the channel, and the base station to transmit the packets to the new user. Also, the control unit may control the existing user to restart the receiving operation when the control unit detects a voice portion of the channel, and the base station to stop the transmission of the packets to the new user. In addition, the base station preferably allocates a spreading code to the new user in response to the packet receiving request.
Alternatively, when the channel is a data channel, the base station may allocate a spreading code and a time slot to the new user in response to the packet receiving request. In this case, the base station includes a buffer in which the packets are buffered. Also, the control unit may control the base station to transmit the packets to the new user using the time slot based on a storage situation of the packets in the buffer. In addition, the control unit preferably monitor a transmission situation to another existing user via another channel in response to the monitor request, and controls the new user to receive the packets. The base station transmits the packets to the new user in response to the control to the new user by the control unit.